Portable water treatment method

ABSTRACT

A method that can be used in a portable system and apparatus to effectively and efficiently treat aqueous fluids by quickly and reliably adjusting and controlling the free residual level of disinfectants, contaminants or additives through the addition of one or more treating agents such as oxidizing chemicals and/or other special-purpose additives, and that can continuously store, log, retrieve and report the related fluid composition data and other operating parameters on a real-time basis at either the use site or a remote location. A preferred use for the subject method is managing the chemistry of disinfectant, contaminant and/or additive levels in aqueous fluids used in hydraulic fracturing operations, and controlling the free residual levels of the disinfectant or contaminants within the fluids, including fluids maintained in frac tanks during temporary cessation of a hydraulic fracturing operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for treating at least one stream ofaqueous fluid to a defined free residual level of one or morecontaminants or other undesirable substituents by using the portablesystem and apparatus disclosed herein to control introduction of atleast one oxidizing chemical, preferably chlorine dioxide, either aloneor in combination with other additives. One preferred embodiment of theinvention relates to a method for treating water intended for use inindustrial, agricultural, food processing, oil and gas, or otherapplications. More specific examples of such uses include withoutlimitation for treating industrial cooling water, HVAC cooling water,fruit and vegetable wash water, or poultry wash water, primary andsecondary disinfecting of potable water, and treatment of aqueous fluidsfor subsurface applications such as disinfection, drilling, fracturing,well stimulation, sour well conversion, and well cleanout. Oneparticularly preferred embodiment of the invention relates to a methodfor analyzing and treating source water and produced water (individuallyor collectively, “frac water”) used in hydraulic fracturing fluids(“frac fluids”) or aqueous fluids used in other processes for oil andgas wells.

2. Description of Related Art

The use of various oxidizing chemicals and non-oxidizing chemicals fortreating water and, more particularly, for treating water used in fracfluids is well known. Because such fluids are routinely injected intowell bores and subsurface formations, the possibility always exists thatsome leakage into the underground water table can occur. Some prior artsystems and methods have disclosed introducing chlorine dioxide intofracturing fluids downstream of the fracturing fluid holding tanks(“frac tanks”) or forming it in situ downhole. These methods of additionhave many disadvantages including, for example, less ability to controlthe chemical addition or to verify the additive concentration in thetreated fluid, lack of portability, lack of a homogeneous blend, limitedeffectiveness due to pH of the water going downhole, and insufficientcontact time or concentrations to kill bacteria. To applicants'knowledge, no one else presently treats the aqueous component of fracfluids upstream of the frac tanks.

A portable system, method and apparatus are therefore needed foreffectively and economically treating source water and produced water toa defined free residual level of chlorine dioxide or other oxidizingchemical that ranges from about 0.25 to not greater than about 25 ppmdepending upon application and situation. Other beneficial advantagesachievable through use of the invention disclosed herein include, forexample, the capability for reliably controlling the chemistry of andadditive levels in treated water; for safely generating chlorine dioxidein a controlled environment; for independently recirculating, treatingand adjusting the chemistry of and additive levels in fluids maintainedin individual frac tanks; and, if a leak or overflow of a frac tankoccurs, minimizing the amount of treating chemical that is released tothe environment with far less harmful environmental impact than wouldlikely be experienced if using traditional water treatment chemistriesand methods.

SUMMARY OF THE INVENTION

A portable system, method and apparatus are disclosed herein that can beused to effectively and efficiently treat aqueous fluids by quickly andreliably adjusting and controlling the free residual level ofcontaminants through the addition of one or more treating agents such asoxidizing chemicals and/or other special-purpose additives, and that cancontinuously log and report the related fluid composition data on areal-time basis. The entire system and method can be controlled andoperated either from the use site or from a remote location. Suchaqueous fluids can be used for a wide range of applications including,for example, treating industrial cooling water, HVAC cooling water,fruit and vegetable wash water, or poultry wash water, primary andsecondary disinfecting of potable water, and treatment of aqueous fluidsfor subsurface applications such as disinfection, drilling, fracturing,well stimulation, sour well conversion, and well cleanout. As usedthroughout this disclosure and the appended claims, the term “freeresidual level” means oxidizing material available to react withbiological species after background contaminants or demand have beenconverted.

The subject invention desirably includes a capability for monitoring,adjusting, controlling and recording physical and compositionalparameters such as volumetric flow rate, pH, total dissolved solids(“TDS”), chlorine dioxide level, density, salinity, conductivity,oxidation reduction potential (“ORP”), viscosity, temperature andpressure of the aqueous fluid, and concentrations of other detectablecations and anions, and for using the resultant information to determinea preferred treatment rate for each treating agent. Examples of suchdetectable cations include aluminum, ammonium, barium, calcium, chromium(II, III), copper (I, II), iron (II, III), hydronium, lead (II),lithium, magnesium, manganese (II, III), mercury (I, II), nitronium,potassium, silver, sodium, strontium, and tin (II). Examples of suchdetectable anions include simple ions such as hydride, fluoride,chloride, bromide, iodide, and oxoanions such as arsenate, arsenite,thiosulfate, sulfite, perchlorate, chlorate, chlorite, hypochlorite,carbonate, and hydrogen carbonate or bicarbonate. Although the safe orpermitted concentrations of various available oxidizing chemicals canvary, the concentration range of chlorine dioxide that has beendetermined to be safe for human ingestion is less than 5 ppm, with lessthan 0.8 ppm being preferred for potable water. The recently proposed“AWW Standard” (for Angelilli, Wong, Williams) is a more preferredstandard, however, because it is defined in terms of the requirementsunder the relevant U.S. EPA and FDA standards. Under the AWW Standard,chlorine dioxide concentrations ranging from 0.25 up to 5 ppm arepreferred for fluids pumped downhole, while the chlorine dioxideconcentration for produced water should not exceed 0.8 ppm. For use inthe present invention, operational levels of unreacted chlorine dioxideranging from about 0.25 to about 25 ppm are acceptable, with levelsranging from about 0.25 to about 5 ppm chlorine dioxide, beingpreferred. A low level, such as 0.25 ppm, of chlorine dioxide in anaqueous fluid indicates, for example, that all bacteria have beenremoved and the fluid has been disinfected without totally exhaustingthe supply of the disinfecting oxidizing chemical. The use of additiveconcentration levels higher than 5 ppm, such as up to 25 ppm forexample, is generally preferred where the aqueous fluid is more highlycontaminated or where the bacterial or contaminant load is highlyvariable.

According to one preferred embodiment of the invention, a portablein-line system, method and apparatus are disclosed herein that can beused to blend and treat source water and/or produced water that isutilized in frac fluids pumped into oil or gas wells to reliably controlbacterial contaminant levels within a predetermined range. As usedherein, the term “source water” includes, for example, surface waterfrom a frac water pond, water drawn from different points within aparticular surface water source, trucked-in water, and any other waterthat may be available from an alternative source such as a pressurizedline. The subject frac water management system is intended to operatein-line between the water source and the frac tanks, with the treatingchemicals being introduced through an eductor, primarily utilizing themotive force of the frac water supply pumps to provide the energy forchemical mixing. Alternatively, auxiliary pumps can be used if desiredfor introducing oxidizing chemicals or other additives into the flowingfrac water. The system, method and apparatus of the invention can beused to proportionally blend source and produced water, source waterfrom different sources or pick-up points, and source water or producedwater in combination with a flow of previously treated frac water asdesired.

As used throughout this disclosure and the appended claims, the term“portable” means transportable either by towing or by mounting on or inone or more trailers or motor vehicles so as to provide a self-containedtreatment and monitoring system that is rapidly connectable to providein-line access to other fluid flow lines, devices or equipment. In thecontext of flow lines, devices or equipment used to implement ahydraulic fracturing operation for an oil or gas well, “portable”includes everything needed to install and operate the system, method andapparatus disclosed herein between frac water supply pumps and fractanks that are already in place. In this context, it should beappreciated, however, that produced water held in a “flow-back” tanklocated among or nearby frac tanks should be viewed as part of theaqueous fluid supply system that is disposed upstream of the system,method and apparatus of the invention.

According to another preferred embodiment of the invention, a producedwater management system is also provided. Produced water is preferablyblended into other source water provided to the system and apparatus ofthe invention prior to treatment of the frac water in accordance withthe method of the invention. A proportional mixing system is disclosedthat facilitates such blending in accordance with the objective oftreating the resultant mixture to produce treated water having a definedfree residual level of contaminants below a predetermined maximum levelor within a predetermined range. Using this invention, the water inputto a hydraulic fracturing operation can be managed according toparameters and concentrations of detectable cations and anions asidentified in paragraph [0005].

The use of sequential treatment points for introducing more than onetreatment chemical or additive into a single pressurized flow of aqueousfluid or for introducing a single treatment or additive at sequentiallyspaced points in a single pressurized flow upstream of the frac tanks isalso included within the scope of the present invention. The ability toreact in real-time to a changing volume of aqueous fluid or toselectively define the volume of aqueous fluid to be treated using thesystem, method and apparatus of the invention are both elements of theinvention that can be important to achieving operational success andconsistently positive outcomes.

According to another preferred embodiment of the invention, an oxidizingchemical agent is used to treat bacterial or other biologicalcontaminants present in frac fluids. A preferred oxidizing chemicalagent is chlorine dioxide, although other similarly effective oxidizingagents such as ozone, peroxides and persulfates can be similarly used atvarying concentrations with varying results for some applications.Chlorine dioxide is preferably generated in situ within the system andapparatus of the invention from chemical precursors, the preferredmethod of which includes the use of sodium hypochlorite, hydrochloricacid, and sodium chlorite that are introduced into the reactor in liquidform and that react upon contact with each other in an acidic aqueousenvironment generally having a pH of less than about 6. The oxidizingchemical is preferably introduced into a zone of turbulent flow of thefrac fluid through an eductor disposed upstream of the frac tanks,thereby achieving better mixing and better contact with the particularcontaminant(s) then being treated. The treatment rate is preferablyregulated automatically by a self-modulating stoichiometric controllerthat varies the amount of oxidizing chemical delivered to the aqueousfluid stoichiometrically depending upon demand. Use of the system andapparatus of the invention in accordance with the subject method canproduce “kill rates” of biological contaminants that typically exceed99.99%.

By introducing treating chemical or additive into a sidestream drawnfrom the main flow of pressurized aqueous fluid in accordance with onepreferred embodiment of the invention, it is possible to reduce thelikelihood or a possible adverse effect or outcome from “overshooting”the target concentration of the chemical or additive. This technique isfacilitated by the use of a “PID loop” (process value, interval andderivative) or proportional independent digital control (“fuzzy logic”)system in the design, implementation and use of the present invention.

According to another embodiment of the self-contained apparatus of theinvention, integral safety devices are desirably provided that areautomatically activated to warn workers of any dangerous level ofchlorine dioxide and to isolate the chlorine dioxide generator of theinvention, neutralize and purge the apparatus with sodium sulfitewithout exposure to chlorine, caustic, or otherwise harmful chemicals.Audible and visual alarms, a safety stop and two isolation valves,preferably tritium ball valves, are desirably provided for each reactor.A flow sensor and pressure gauge also provide real-time input to thesafety devices used in conjunction with the chlorine dioxide generator.A specially modified PVC cleanout for the chlorine dioxide reactor isalso provided.

According to another preferred embodiment of the system and apparatus ofthe invention, a portable distribution manifold is provided upstream ofthe frac tanks in a hydraulic fracturing operation, which manifold canbe selectively used in accordance with the method of the invention tointroduce treated water into one or more frac tanks, or to recirculatefrac fluid disposed in one or more tanks for possible further treatment,particularly during periods when hydraulic fracturing operations areshut down or during other quiescent periods when fluid maintained in oneor more frac tanks is otherwise at rest. By recirculating frac fluidsduring such quiescent periods, better homogeneity is maintained withineach tank, less precipitation of suspended solids occurs, and the timerequired to resume hydraulic fracturing operations with a fluid of aknown and reliable composition is significantly reduced. According toanother preferred embodiment of the invention, a frac tank circulationand monitoring system, method and apparatus are also disclosed thatcomprise and utilize at least one auxiliary pump, a separateprogrammable logic controller (“PLC”) and, most preferably, a secondaryinjection point, to precisely trim or control the residual chlorinedioxide level in each frac tank. This capability for continuouslyturning the water over and for monitoring and trimming the chlorinedioxide or other additive levels in each frac tank also enables thesystem operator to control compositional parameters in each frac tankeven when the site operator is not performing a hydraulic fracturingoperation in the associated well(s). Auxiliary booster pumps aredesirably provided within the system and apparatus of the invention toestablish fluid circulation through the system and apparatus wheneverinlet water supply pumps are not operating during shutdown of thehydraulic fracturing operation. Use of the auxiliary circulation systemcan also provide freeze protection during otherwise quiescent periods inwinter. Because the composition of the frac fluid in each separate fractank, including the associated contaminant and additive levels,typically varies, use of the subject circulation and monitoring systemof the invention facilitates management of the water chemistry in eachtank.

According to another embodiment of the invention, a new control, datastorage and reporting system is disclosed that has the capability tocontrol operations from either onsite or remote locations and toretrieve and reuse stored data to supplement temporary sensory loss atany point within the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The method of the invention is further described and explained inrelation to the following drawings wherein:

FIG. 1 is a simplified schematic of one preferred embodiment of theportable water treatment system of the invention;

FIGS. 2A and 2B together depict a simplified process flow diagramillustrating one preferred embodiment of the method of the invention;

FIG. 3 is a simplified top plan view of one preferred embodiment of aportion of the portable frac water management system of the invention;

FIG. 4 is a simplified front elevation view of the portion of theportable frac water management system shown in FIG. 3;

FIG. 5 is a simplified diagrammatic view of one embodiment of apreferred chlorine dioxide generation and handling system of theinvention for use in practicing one preferred embodiment of the portablewater treatment system and method of the invention using threeprecursors; and

FIG. 6 is an example of a graphical record and printout generatedaccording to a preferred embodiment of the instrumentation and controlsystem for monitoring chlorine dioxide levels in an aqueous fluidtreated in accordance with the system, method and apparatus of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in simplified form in FIG. 1, portable water treatment system10 utilizes a plurality of inlet water supply pumps 26, 28, 30 and 40supplying water to a portable carriage device, most preferably a trailer12, as defined above. If needed, depending upon factors such as, forexample, the number and size of the flow lines, and the size of trailer12 or such other towable or motorized carriage device as may be used,all or part of the apparatus of FIG. 1 disposed between the water inletlines exiting the pumps and frac tanks 56, 58, 60, 62 can be installedin two or more companion devices such as two trailers, a truck and atrailer, or the like, or can even be skid-mounted for rapid deploymentand installation at a use site. If installed inside a trailer, truck orthe like, the subject apparatus can be installed in modules on racks,rails or skids as needed and secured in place by appropriateconventional or commercially available means.

Utilizing crossover 32, which will contain at least one valve that isnot shown, either or both of pumps 26, 28 can draw source water from aplurality of pick-up points 22, 24 in frac water pond 16. It should beappreciated that valving and instrumentation are not shown in FIG. 1,which is intended to lay out an example of one suitable flow scheme asimplemented at a use site. It should also be appreciated that thechemistry and solids content of the frac water drawn from differentpick-up points in the same frac water pond 16 can vary. Although flowlines 34, 31 from pumps 26, 28, respectively, are depicted as providinga single combined inlet flow to portable treatment system 10, it shouldbe appreciated that more than a single flow line from frac pond 16 toportable treatment system 10 can be provided if desired.

Pump 30 can optionally draw produced water from an auxiliary source suchas a frac tank dedicated to flow-back service, or can draw water fromanother source to provide another pressurized inlet to portabletreatment system 10 as desired. By providing a crossover line 35 with acontrol valve between lines 34 and 36, source water and produced watercan be blended together in any desired proportion prior to reachingportable treatment system 10. If the auxiliary source is alreadypressurized, a bypass line 37 can be provided to bypass pump 30. Ifneeded, still another auxiliary aqueous liquid source such as tank truck42 can be provided. As shown in FIG. 1, pump 40 can recirculate aqueousliquid through tank truck 42, or can pump the liquid directly toportable treatment system 10 through another inlet flow line 38.Although pump 40 is shown as being free-standing, it will be appreciatedthat pump 40 can also be mounted on tank truck 42.

As is discussed in greater detail below, a significant advantage ofportable treatment system 10 of the invention is that inlet water supplypumps 26, 28, 30 are typically already in place at the well site forpumping inlet water to a conventional hydraulic fracturing system. Byproviding quick-connect couplings to the inlet lines that are alreadybuilt in to portable treatment system 10, the hook-up time is minimized.Because the force required to move the frac water through the system andapparatus of the invention is provided by the regular inlet water supplypumps, no additional pumps are required except as described below forother auxiliary portions of the subject system. In a typicalinstallation, the inlet lines to portable treatment system 10 are about10 inches in nominal diameter and carry up to about 6500 gallons perminute at a pressure of up to about 120 psi. This same motive force isdesirably used in a preferred embodiment of the invention to educttreating chemical such as chlorine dioxide, first into a sidestream andthen into the primary fluid flow.

The structure, use and operation of apparatus disposed in trailer 12 inportable treatment system 10 of the invention to treat the source andproduced water in accordance with the method of the invention arefurther described below in relation to FIGS. 2-6. It should beunderstood that the number of individual flow lines and the number ofadditive injection points in each flow line can vary within the scope ofthe invention. Although three separate inlet flow lines 34, 36 and 38are shown entering trailer 12 in FIG. 1, the number can be one or moreand, if desired, an inlet manifold can be provided to proportion anddistribute flow into any one of a plurality of individual flow lines toserve as the primary fluid flow paths through portable treatment system10. One significant advantage of water treatment system 10 is that allthe flow sensors, instrumentation and controls are desirablyelectronically linked to at least one programmable logic controller(“PLC”) and data storage and retrieval unit disposed inside trailer 12and also to at least one PLC and data storage and retrieval unit locatedat some remote site. This control system enables users to operate system10 and to control the method and apparatus of the invention from thewell site or, if needed, from a remote location. Also, while system 10is preferably operated using real-time data, it can also be operatedusing saved operating data and parameters should needs dictate,especially for short periods of time.

Referring again to FIG. 1, following treatment of the water directedthrough the individual flow lines inside trailer 12, two treated waterstreams 44, 46 are shown entering manifold 14. From manifold 14, thetreated water can be selectively discharged through flow lines 48, 50,52, 54 into any one or more of frac tanks 56, 58, 60 or 62,respectively. Although four frac tanks are shown, more or fewer fractanks can be used within the scope of the invention. In conventionalpractice, the chemistry and contaminant level of the various frac tankscan vary greatly, and one or more frac tanks can be dedicated toflow-back water that is recovered from the wellbore subsequent tohydraulic fracturing.

Depending upon the construction of and the flow control system used formanifold 14, the water introduced into frac tanks 56, 58, 60 and 62through flow lines 48, 50, 52, 54 can have the same or differentchemistries as desired, but according to a preferred embodiment of themethod of the invention, all treated water entering any one of the fractanks will have free residual levels of any treating chemical that donot exceed predetermined maximum values.

On the outlet side of frac tanks 56, 58, 60 and 62, outlet flow lines64, 66, 68 and 70 are provided as a flow path for treated frac water tomove to blender 72, where it can be combined with other conventionaladditives such as proppants and the like that are used in hydraulicfracturing fluids. One or more booster pumps, not shown, can be provideddownstream of frac tanks 56, 58, 60, 62 to move treated frac water toand through blender 72 from the frac tanks, and from blender 72 to theprimary injection pump, not shown, for the hydraulic fracturing fluid.Although the flow of fracturing fluid from the frac tanks to the blenderand then downhole is conventional technology and is not part of thepresent invention as narrowly defined, it should be noted thatrecirculation lines 82, 84, 86 and 88 from frac tanks 56, 58, 60, 62,respectively, back to portable treatment system 10 are part of theinvention. The provision and use of system 10 having the capability ofselectively recirculating and treating fluid from any one or more of thefrac tanks by the use of one or more auxiliary pumps (seen in FIG. 2B),even when all of primary pumps 26, 28, 30, 40 are shut down, enables anoperator to consistently maintain the same or different fluidchemistries in each frac tank as desired. It should be understood andappreciated that individual recirculation lines 82, 84, 86 and 88 can beused to carry fluid back to the chemical treating portion of system 10independently, or can be consolidated into a single return header asdesired, providing such pumps as may be required to implement suchvarious flow schemes.

Unlike conventional hydraulic fracturing systems, frac water treatmentsystem 10 of the invention provides the capability for intermittently orcontinuously recirculating aqueous liquid from each individual frac tankback to the water treatment trailer, where the water chemistry andadditive levels in each frac tank can be adjusted as desired. Auxiliarypumps are desirably provided inside portable treatment system 10 toprovide motive force for the recirculation. Such recirculation helpsprevent settling of solids into the bottom of each frac tank, promotesmixing and homogeneity of the fluid inside each tank, and providesfreeze protection at low ambient temperatures. The ability to maintaindesirable water chemistry and additive levels in each frac tank asdesired during periods of inactivity when hydraulic fracturingoperations are not underway reduces the start-up time otherwise requiredwhen activities resume and provides a more consistently reliable fracwater source than has previously been available to those engaged indrilling and production. Frac water recirculated from the frac tanks toportable treatment system 10 and treated in accordance with the methodand apparatus of the invention as are further described below inrelation to FIGS. 2-6 is desirably returned to frac tanks 56, 58, 60 and62 through recirculation return lines 74, 76, 78 and 80, respectively.It should be appreciated by those of skill in the art upon reading thisdisclosure that the system, method and apparatus of the invention willenable an operator to discharge treated aqueous fluid directly into anyselected frac tank, or to discharge treated fluid into manifold 14 fromwhich it can also be distributed into any one or more frac tanks asdesired.

Where one or more frac tanks are used to hold flow-back or producedwater, that water can be recirculated to portable treatment system 10and proportionally blended into source water as previously described, orcan be separately treated and returned to the flow-back tank asdescribed above for the recirculated aqueous liquids. In the formercase, the treated produced water flows into manifold 14 with the othertreated source water, and in the latter case, the treated produced waterflows directly back into the flow-back or produced water tank.

Generally speaking, the method of the invention includes determining theinlet flow rate and an initial set of fluid properties and compositionalparameters for the incoming frac water. Such parameters can include, forexample, volumetric flow rate, pH, TDS, chlorine dioxide level, density,salinity, conductivity, ORP, viscosity, temperature and pressure of theaqueous fluid, and concentrations of other detectable cations andanions, and for using the resultant information to determine a preferredtreatment rate for each treating agent. Examples of such detectablecations include aluminum, ammonium, barium, calcium, chromium (II, III),copper (I, II), iron (II, III), hydronium, lead (II), lithium,magnesium, manganese (II, III), mercury (I, II), nitronium, potassium,silver, sodium, strontium, and tin (II). Examples of such detectableanions include simple ions such as hydride, fluoride, chloride, bromide,iodide, and oxoanions such as arsenate, arsenite, thiosulfate, sulfite,perchlorate, chlorate, chlorite, hypochlorite, carbonate, and hydrogencarbonate or bicarbonate. Except for the flow rate through thelarge-diameter pipes, most of the fluid properties and compositionalparameters are desirably determined in, and treating chemicals andadditives are desirably introduced into, sidestreams of reduced flowthat are diverted into and out of the primary flow lines through lateralwyes. To the extent possible, the relevant properties and parameters aredetermined using in-line sensors and gauges, with valves and sampleports provided as needed to facilitate data and sample collection, andquality control.

By managing the chemistry and composition of frac water upstream of thefrac tanks in accordance with the method of the invention, severaloperational benefits are achieved. Once the initial water properties andparameters are determined, set points are chosen and verified for theconcentrations of treating chemicals and additives to be introduced intothe fluid flow before the frac water reaches the frac tanks. Accordingto one preferred embodiment of the invention, each treating chemical orother additive (and especially where chlorine dioxide is the primarytreating chemical) is introduced in two sequential increments in twodifferent sidestreams that are longitudinally spaced apart along theflow path of each primary flow line. Treating chemicals and additivesare desirably introduced into the primary flow lines in regions ofturbulent flow to facilitate dispersion. One or more PLCs are desirablyused to calculate the addition rates needed to produce a desired finalconcentration of each treating chemical and additive in the treatedwater that exits the system, and to operate the valves as needed toachieve the desired final concentration. In some cases, treated fluidcan be recirculated through the treating apparatus of the invention toincrementally adjust the concentration of treating chemicals oradditives to a desired level.

Through use of the method of the invention, which can be implemented ina preferred embodiment with the portable system and apparatus asdisclosed herein, users can now exercise control over the composition ofaqueous fluids in ways not previously achievable using conventionalwater treatment methods. For example, the method of the inventionenables one to make real-time adjustments to the concentration oftreating chemicals and additives in a pressurized flow of aqueous liquidin response to changes in composition of the incoming source water, nomatter whether such compositional changes are attributable to differentliquid sources or pick-up points, different degrees of contaminationwith differing treatment demands, different types and sources ofcontaminants, or the like. Similarly, the subject method enables onepracticing the invention to target and maintain a desired concentrationof a particular treating chemical or additive in a pressurized aqueousflow by the sequential addition of differing amounts of the chemical oradditive coupled with systematic monitoring and comparison to thebenchmark level to determine the desired magnitude of the nextcompensating adjustment. Use of the subject method also enables anoperator to maintain control over the composition of an aqueous streamfrom the use site or from a remote location and, when the flow ofaqueous liquid is interrupted for whatever reason, to continuerecirculating an aqueous liquid to monitor and/or treat the fluid asnecessary in response to a demand, target concentration, or other suchparameter.

As applied to fracturing operations for oil and gas wells in particular,the subject method can be implemented to allow an operator to achievemany different objectives. Such objectives include, by way ofillustration and not of limitation, to proportionally blend source andproduced water, to treat either inlet stream independently of the other,to treat a combined inlet stream, to treat with one or more oxidizingchemicals either alone or in combination with other additives such asscale and corrosion inhibitors, to retreat sequentially with a singlechemical or additive, to selectively direct treated water to and througha distribution manifold that is part of the subject system and that islocated upstream of the frac tanks, to selectively recirculate a portionof the treated liquid to be reintroduced into the inlet stream toretreat or to help balance the composition and chemical or additiveconcentration of the incoming stream, to achieve a targeted chlorinedioxide concentration in frac water, and to recirculate throughindividual frac tanks to maintain, balance or vary the water chemistryand concentrations of chemicals and additives in various frac tanks.

A preferred method for introducing treating chemical such as chlorinedioxide and additives such as scale inhibitor and corrosion inhibitorinto the frac water flowing through the apparatus of the invention is byuse of at least one eductor installed in fluid communication with eachside stream in which treating chemical or additive is to be introduced.Alternatively or supplementally, one or more treating chemicals and/oradditives can be introduced into the fluid flow using small volumepositive displacement injection pumps. The treating chemicals oradditives introduced into the frac water using the method of theinvention can be produced in situ or can be provided in usablequantities or amounts from other sources and stored inside the traileror in another carriage device that is consistent with applicable storageand handling requirements or regulations and also compatible with theobjectives of portability, effectiveness and efficiency duringtransportation and use of the system, method and/or apparatus of theinvention. Such storage means can include, for example, drums, totes,tanks or other containers of appropriate volume in combination with suchchemical transfer devices and ancillary controls and safety precautionsas are known to those of ordinary skill in the art to be desirable ornecessary for the particular conditions or circumstances of use.

A preferred treating chemical for use in the method of the invention ischlorine dioxide, and a preferred method for providing chlorine dioxideto the frac water treatment system of the invention is generating it insitu inside a reactor system that further comprises a dedicated PLC, areaction chamber with a dedicated alarm and safety system, and a purgeand cleanout system. The use of two or more treating chemical reactorsor generators is preferred in practicing the method of the invention.Chlorine dioxide can be provided or generated using one, two and threeprecursor systems and appropriate reactors that are commerciallyavailable from various manufacturers or suppliers. A preferred reactorfor use in practicing the method of the invention can be used togenerate chlorine dioxide from three precursors that meet in liquid formand react in the presence of water sprayed into the reactor. Threepreferred precursors are sodium hypochlorite, hydrochloric acid andsodium chlorite. A preferred alarm and safety system for use in theinvention comprises both audio and visual alarms, pressure gauges, andremote and onsite automatic and manual safety stop valves that isolatethe reactor on both the inlet and outlet sides. A preferred purge andcleanout system includes a sensor-activated sodium sulfite purge and aPVC cleanout that is located above the reactor and is resistant tocorrosion and degradation (better than stainless steel) when used inthis application. Sodium sulfite is particularly preferred for use inpurging the reactor system because of its high, virtually infinite,solubility in chlorine dioxide, and sits on top of the reactor.

One preferred method of the invention is further described in relationto FIG. 2, wherein source water 202 is supplied to primary flow line 220from a frac pond or another other pressurized line source. It will beappreciated that conventional, commercially available control valves,check valves, back-check valves, flow meters, gauges, indicators,transducers, transmitters, controllers, control lines, tees, wyes,safety stops, alarms, indicator lights, and the like that are well knownto those of skill in the art for implementing a method such as thatdescribed herein are not shown in FIG. 2, which is primarily intended todescribe the process flow through the system and apparatus of theinvention. More particular mechanical descriptions are provided inconnection with FIGS. 3-5 below, which are more narrowly directed toimplementation of the chlorine dioxide generation aspect of theinvention and introduction of the treating chemicals and additives intothe primary flow lines by use of an eductor.

Although only one primary flow line is shown in FIG. 2A, it should beappreciated that two or more primary flow lines can be operated inparallel within the scope of the invention. Produced water 204 issimilarly introduced through line 209 into primary flow line 220.Because frac water supply pumps (seen in FIG. 1) are already in place atmost well locations, the system and apparatus of the invention can beinserted and connected downstream of the supply pumps and upstream ofthe frac tanks to pretreat the frac water in a way not previouslyachievable and using the motive force already in place to move theaqueous fluid through the water treating system.

Scale inhibitor 210 can be introduced into the produced water throughline 211 because of the relatively high proportion of mineralcontaminants likely to be contained in produced water 204. Scaleinhibitor 210 can be introduced into the pressurized flow of producedwater using a commercially available injection pump or by the use of aneductor disposed at the inlet into the flow of produced water 204.Similarly, although not shown in FIG. 2A, it will be appreciated thatcorrosion inhibitor or other additives or chemicals can likewise beintroduced into produced water 204 or directly into primary flow line220 if needed. Side streams 206, 212, 216 having reduced flow can beprovided if desired to facilitate the placement and use of sensors 208,214, 218 for determining flow parameters and compositions as needed.

The primary flows as exemplified by primary flow line 220 each passthrough control valves having onsite or remote indicators that displaythe inlet water flow rates and TDS for each flow. All necessary flowmonitoring and control systems are desirably capable of being powered bya self-contained power source such as a combination of auxiliarybatteries and generators supporting the system and apparatus of theinvention, although AC power can also be provided onsite from remotegenerators or other available electrical power sources in many cases andconverted to DC power where required. Sensors 214 can comprise pressuregauges and flow rate and set point indicators that are linked to valvesthat control the optional flow of scale inhibitor into produced water204. Flow rate and set point indicators similarly control the proportionof produced water 204 that is combined with source water 202 intoprimary flow line 220. The aqueous fluid supply lines can also beprovided with control valves and safety valves having status indicatorsand alarms as needed.

Sensors 228 in side stream 226 whose inputs are directed to at least oneon-site and at least one remotely located PLC 215 linked with flow rateand set point indicators and control valves determine the flow 224 ofinlet water to one or more chlorine dioxide generators 230. Each PLC 215is also desirably linked to a data storage and retrieval unit 217 thatis capable of providing operational inputs to PLC 215 from stored dataif needed due to instrument failure or other circumstances. Eachchlorine dioxide generator 230 preferably produces chlorine dioxide fromprecursors 232, 234 and 236 that preferably include sodium hypochlorite,hydrochloric acid and sodium chlorite. Although a three-precursor systemand the generation of chlorine dioxide within the confines of theportable apparatus of the invention are preferred, it will be understoodby those of skill in the art upon reading this disclosure that otherdevices and systems for providing chlorine dioxide or other oxidizingchemicals can also be used to practice the subject method, such as forexample, 1- or 2-precursor systems for generating chlorine dioxide. Theuse of in situ generation of chlorine dioxide in combination with theuse of an eductor instead of injection pumps to introduce the treatingchemical into a pressurized flow of aqueous liquid such as frac waterhas proved to be an efficient and effecting method for managing a fracwater treatment system.

Chlorine dioxide generator 230 is desirably provided with safety valvesand alarms suitable for isolating the generator in case of anoperational failure or unsafe condition. A sodium sulfite purge 240 isdesirably provided above generator 230 to flood the chlorine dioxidegenerator in case of emergency, and cleanout 238 is provided for use incleaning and restarting the reactor, especially following an emergencyshutdown. Treated water flow 242 exiting chlorine dioxide generator 230can be selectively controlled and directed back into primary inlet waterflow 220 through line 243 by control valves having status indicatorsvisible at a proximal and/or remote control panel, with the flowparameters and treating chemical concentration being determined andindicated by sensors 246 disposed in side stream 244.

A further aspect of the method of the invention relates to frac tankmonitoring. According to one preferred embodiment of the invention, aseparate controller is provided for each frac tank, and each frac tankis provided with a secondary injection point to precisely trim orcontrol the residual level of chlorine dioxide or other treatingchemical or additive in that frac tank. Referring to FIG. 2B, treatedwater flowing through line 242 can also be selectively distributedthrough any or all of inlet lines 248, 250, 252 and 254 to frac tanks256, 258, 260, 262, respectively. Treated water entering primary flowline 220 through line 243 flows into the manifold that is also part ofthe invention, through which the treated water can be selectivelydistributed to any or all of frac tanks 256, 258, 260, 262 through inletlines 290, 292, 294 and 296, respectively.

Referring again to FIG. 2A, one or more other treating chemicals oradditives 304 can be introduced into primary inlet water flow line 220using side stream supply line 302, return line 310, each of which can befully instrumented by one or more sensors 308, 314. Side stream 298 andsensors 300 affords an opportunity to monitor the affect of additives304 on the primary water flow. Generally speaking, various commerciallyavailable friction reducers are known to have associated chlorideconcentration ranges within which they are most effective. For example,some friction reducers are effective at chloride concentrations rangingup to 125,000 ppm and beyond, while many others are not effective atsuch high chloride concentrations in the treated fluid and are preferredfor use only within a lower and narrower range of chlorideconcentrations. Accordingly, by using the method of the invention, onecan choose a chloride set point at which a given friction reducer isknown to be effective, and then use the system of the invention to blendinlet water from various sources to manage the chloride content of thefluid being treated within the effective range of that friction reducer.If for any reason the average chloride concentration of the source wateror produced water changes substantially, it may become necessary toselect a different friction reducer and/or a new chloride concentrationset point that will accordingly adjust the amount of friction reducerbeing introduced into the flow through the system of the invention. Itshould be appreciated that this example is merely illustrative ofbenefits and advantages that can be achieved through use of the presentinvention, and that other benefits are likewise available by selectivelyadjusting either the blend of inlet water and other aqueous fluid beingsupplied to the chemical treatment section of the invention, or byselectively adjusting the type and amount of chemical treatment that isintroduced into the fluid flow line.

Referring to both FIGS. 2A and 2B, frac tank recirculation lines 276,278, 280 and 282 can be controlled to selectively discharge a controlledflow of frac water into tank recirculation line 284 that utilizeauxiliary pump 283 to introduce the recirculated fluid into flow line220 above take-off lines 224, 302 for injection of chlorine dioxide 230and the other additives 304, respectively. Side stream 286 with sensors288 is again provided to monitor and report to the PLC the flowparameters and chemistry of the recirculated aqueous liquid. Thisrecirculation loop affords the user the opportunity to continuouslyreadjust the chemistry and additive concentration levels of therecirculated fluid.

During hydraulic fracturing operations, frac water is selectivelywithdrawn from the individual frac tanks through lines 264, 266, 268,270 using existing technologies and is discharged into blender 274,where it can be mixed with other fracturing fluid components and thenpumped downhole as indicated by arrow 274.

An illustrative primary flow configuration through trailer 12 as shownin FIG. 1 is depicted in FIGS. 3 and 4, and an illustrative sidestreamflow through a chlorine dioxide introduction loop 450 is depicted inFIG. 5. Although a substantially linear piping layout is shown in FIGS.3-4, it should be appreciated that the primary flow path can also belooped, for example, if needed due to space restrictions in a particulartrailer 12 or other carriage device, and that the number of flow linesis not limited other than by space considerations. Referring first toFIGS. 3 and 4, piping and instrumentation comprising two parallel andsubstantially identical primary fluid flow paths embodied in lines 404,408 for pressurized source water flows 442, 446, respectively, are shownfor illustrative purposes. Each primary source water flow line ispreferably connectable at its inlet end to one of the source waterinlets as previously described, and at its outlet end to an outlet lineflowing to manifold 14 disposed inside trailer 12 or between trailer 12and the existing frac tanks as seen in FIG. 1. Flow line 406, shown heredisposed between lines 404 and 408, supplies a flow of pressurizedproduced water as indicated by arrows 444.

Referring again to the illustrative apparatus of the embodiment of theinvention as depicted in FIGS. 3-4, and particularly with regard toprimary flow lines 408, female inlet coupling 440 is attachable, forexample, to a source water supply line. Flow meter 424, preferably aMagMeter, is supplied at the inlet end, upstream of lateral wye 438,which redirects a relatively minor portion of the flow through valve 436into line 434. The side stream thereby created can be used to introduceany additive such as, for example, a corrosion inhibitor, into the flowof source water. Following introduction of the additive, the side streamis reunited with the primary flow through line 408 through line 430,valve 428 and lateral wye 426. The flow scheme and instrumentation forflow line 404 is substantially identical to that of flow line 408.

Referring next to produced water flow line 406, after flow 444 passesthrough the quick-connect female coupling and flow meter, a portion ofthe flow is similarly redirected through wye 448 and valve 450 into line454. In this case, line 454 can be used for the introduction of a scaleinhibitor, for example, as previously discussed in relation to themethod of the invention. It should be understood and appreciated,however, that other types of additives or treating chemicals couldlikewise be introduced into flow 444 of produced water through this sidestream. Following reintroduction of the side stream flow through line456, valve 458 and lateral return wye 460, flow 444 passes into tee 462,where the flow is redistributed by control valves 468, 470, preferablyconnected to a PLC, and smaller tees 464, 466 into source water flowlines 404, 408, respectively. Safety valves 472, 474 are also desirablyprovided in tee 462.

Downstream of the point of combination of treated produced water flow444 with the treated source water flows 442, 446, lateral wyes 414, 422are again provided in each of flow lines 404, 408. Referring again toline 408, and assuming for illustrative purposes that lateral wye 422 isintended to create a side stream for an injection point for chlorinedioxide, line 420 directs a sidestream that is identified in FIG. 5 byarrow 452 to the inlet side of one of three substantially identicalchlorine dioxide manifolds 481, 483, 485 that are depicted at the leftside of FIG. 5. The inlet flow of the sidestream passes through inletvalve 454, flow meter 458, chlorine dioxide sensor 460, ORP sensor 462,pH sensor 464, temperature and TDS sensor 466, past flow sensor 470,back-check valve 472, scale inhibitor injection point 474, past chlorinedioxide eductor 492, through valve 496, and back to return line 420 ofFIG. 3 as indicated by arrow 498 in FIG. 5.

Referring to the right side of FIG. 5, chlorine dioxide precursors 476,478 and 480, preferably comprising sodium hypochlorite, hydrochloricacid, and sodium chlorite, respectively, are introduced into chlorinedioxide generator 484 that incorporates each of the subsystemspreviously discussed. Chlorine dioxide produced in generator 484 exitsthrough an outlet manifold as indicated by arrow 486 and flows through amotor operated control valve 488 into eductor 492. The flow of fracwater containing the chlorine dioxide introduced into the sidestreamthrough eductor 492 flows through outlet valve 496 and out of thetreatment loop as indicated by arrow 498. As previously discussed inrelation to FIG. 2, chlorine dioxide generator 484 is desirably providedwith safety valves, alarms (preferably onsite and remote audio andvisual alarms), and a purge system 485 and cleanout 487.

Referring again to FIG. 3, the returning flow of chemically treated fracwater can be reintroduced into primary flow line 408 through a returnline, valve and lateral wye (not shown), or can be diverted directly toa frac tank as previously described. Valve 418 is desirably provided tocontrol downstream flow. Where the flow from the treated side streamre-enters primary flow line 408, turbulence is created that promotesdispersion and mixing of the chlorine dioxide throughout the sourcewater flowing through line 408. Referring to FIG. 4, it is seen thatlateral return wye 426 is a dual wye provided with two return positionsso that the return flow can be further distributed if desired.Similarly, a dual wye can be used on the take-off side where the same ordifferent additives are to be introduced at a single point in the flowstream. A principal purpose for creating another sidestream flow is toprovide a secondary point for introduction of chlorine dioxide using achlorine dioxide manifold as described above in relation to FIG. 5.Other sidestream flows can be similarly created for use in introducingother treating chemicals or additives into primary flow line 408, eitherby means of other sampling and eductor loops, or by sidestream loopsutilizing injection pumps. In some situations, particularly where aportion of the primary frac water flow has been recirculated andintroduced into primary flow line 408 from one or more individual fractanks, the inlet flow to a treating chemical or additive introductionsidestream may be obtained from the use of multiple wyes and sidestreams.

Referring to FIG. 6, graphical report 500 is merely an illustrativeexample of the type of data than can be routinely gathered and of areport that can be generated using the system, method and apparatus ofthe invention. Graph 502 is a plot of chlorine dioxide concentration(ppm) over an indicated time interval, with separate plots 504 for eachof four different frac tanks. Table 506 records by tank the treatmentchemical (chlorine dioxide) being used, and the minimum, maximum andaverage chlorine dioxide concentrations (ppm) recorded for each tank.Table 508 records the minimum and maximum chlorine dioxideconcentrations overall that were recorded during the reporting periodfor the four tanks. Use of portable water treatment system 10 asdisclosed herein will not only provide operators with greaterreliability and tighter control over chemicals and additives injecteddownhole, but will provide an accurate historical record of thechemistry and composition of the frac water pumped downhole should aneed arise to establish such information in a reliable, systematic andtrustworthy format.

In conclusion, the present invention allows the trending and correlationof other systems to help advance the chemistry of any subject processand the complete control and automation of the fluid entering into thehydraulic fluid fracturing process. The subject system can react to theever-changing conditions of the fluid in each of the manifold's pipessince the fluid may be from more than one source and or differentpick-up points from each source. The pumps pressures and fluid flowrates can also vary from pump to pump.

According to a preferred embodiment of the invention as disclosedherein, chlorine dioxide manifold 450 as disclosed in relation to FIG. 5has in each of its three separate inlet lines a MagMeter as flow meter458 to measure flow rates, a programmable flow switch 470, a series ofvalves on the inlet and outlet of each pipe, a special injection plateand/or fittings for chemical additions, and an inlet and outlet for aside stream flow of water that allows for the monitoring of thechemicals that are being introduced through the manifold. The manifoldwill measure the flow rate of fluid through the piping manifold in GPM,CFS, LPM, and may be converted into any quantifiable measurement andreports this locally and/or remotely. The subject manifold 450 relies onpressurized water flow from existing frac water pumps but auxiliarypumps 456 can be provided for recirculating fluids to the frac tanks.Flow meter 458 detects flow of fluid and sends a signal based on anymeasurement (such as “show flow when >1 GPM and “no flow” when <1 GPM)that is programmable set point and reports this locally and/or remotely.

With a series of valves and supply line outlets and return line inlets,portable treatment system 10 can divert a sidestream of fluid and flowthat fluid to any other type of chemical treatment and monitoringprocess. In manifold 450, which will also allow for other chemicaltreatments to be injected directly into the manifold, each of the linesis independent from the others and therefore there are at least threeseparate systems and/or processes that all can work at the same time.

Manifold 450 will also allow for chemical treatments that are beinginjected into each line of the manifold to be injected in at one and/ormultiple points so as to evenly distribute the chemistries into theprimary flows of frac water through portable treatment system 10. Thisallows for a quicker reaction and a homogeneous blend between thechemistry and the ever-changing characteristics of the water.

Manifold 450 allows each 10-inch line to be treated differently andindependently from the others. Since the water flowing through themanifold may not be from the same source and/or if from the same sourcethe pick-up points may cause a variation in the water's characteristics.

Through use of the system, method and apparatus disclosed herein,control, adjustment, feed rates, spill detection remote control andcalibrations of all chemicals for any and all part of the inlet fluidson a hydraulic fracturing process. The actual flow rate of fluid to betreated and the total quantity of fluid treated during each phase of theprocess and a total at the end of each process. Chemistries are bestadded in ppm based on actual fluids being used and no one is believed tobe doing this.

Other alterations and modifications of the invention will likewisebecome apparent to those of ordinary skill in the art upon reading thisspecification in view of the accompanying drawings, and it is intendedthat the scope of the invention disclosed herein be limited only by thebroadest interpretation of the appended claims to which the inventorsare legally entitled.

1. A method for producing and continuously monitoring and controlling aconcentration of chlorine dioxide in an aqueous fluid that is present ata well site, which aqueous fluid is adapted hydraulic fracturing, themethod comprising: providing at the well site a continuous, pressurizedflow of the aqueous fluid through at least one fluid flow line from atleast one source of aqueous fluid to at least one frac tank;continuously determining the flow rate of the pressurized flow of theaqueous fluid; continuously determining an initial concentration of thechlorine dioxide within the pressurized flow of the aqueous fluid;continuously determining a treating rate capable of adjusting theinitial concentration of the chlorine dioxide to a defined free residuallevel based upon stoichiometric demand; automatically generating at thewell site sufficient chlorine dioxide solution to achieve the definedfree residual level; treating the aqueous fluid at the well site byautomatically introducing the chlorine dioxide into the aqueous fluid atthe determined treating rate at an initial in-line treatment point underconditions conducive to thorough mixing of the chlorine dioxide withinthe pressurized flow of at least a portion of the aqueous fluid toproduce treated aqueous fluid; continuously monitoring a post-treatingconcentration of the chlorine dioxide within the pressurized flow of thetreated aqueous fluid; continuously comparing the post-treatingconcentration of the chlorine dioxide to the defined free residuallevel; and selectively adjusting the post-treating concentration at thewell site by recirculating at least a portion of the treated aqueousfluid from the at least one frac tank to a point upstream of where theaqueous fluid is treated.
 2. The method of claim 1, comprisingrecirculating the treated aqueous fluid until the post-treatingconcentration of chlorine dioxide is acceptably close to the definedfree residual level.
 3. The method of claim 1 as monitored and managedby at least one programmable controller from either a remote location orat the well site.
 4. The method of claim 1 wherein the post-treatingconcentration of chlorine dioxide is selectively adjusted by injectingadditional chlorine dioxide into the treated aqueous fluid at one ormore treatment points disposed downstream from the initial treatmentpoint.
 5. The method of claim 1 wherein at least a portion of therecirculated treated aqueous fluid is introduced into the pressurizedflow of aqueous fluid upstream of the initial treatment point.
 6. Themethod of claim 1 wherein a scale inhibitor is also injected into thepressurized flow of aqueous fluid.
 7. The method of claim 1 wherein thepressurized flow of aqueous fluid is divided into at least one primarystream and at least one side stream, and wherein the chlorine dioxidesolution is introduced into the at least one side stream.
 8. The methodof claim 1 wherein the aqueous fluid is selected from the groupconsisting of source water, produced water, fluid recirculated from theat least one frac tank, and mixtures thereof.
 9. The method of claim 8wherein at least one frac tank contains source water that is producedwater.
 10. The method of claim 1 wherein the aqueous fluid comprisessource water received from at least two different sources.
 11. Themethod of claim 1, further comprising providing at least one motorvehicle or towable carrier unit within which the chlorine dioxide ismade and introduced into the pressurized flow of aqueous fluid andwherein the post-treating concentration is continuously monitored andselectively adjusted.
 12. The method of claim 11 wherein at least onefluid flow line is looped or coiled within the at least one motorvehicle or towable carrier unit.
 13. The method of claim 1 wherein theat least one frac tanks is a plurality of frac tanks and at least partof the recirculated treated aqueous fluid is recirculated selectivelyfrom at least one of the plurality of frac tanks.
 14. The method ofclaim 13 wherein the aqueous fluid is recirculated intermittently. 15.The method of claim 1 wherein the aqueous fluid is selectivelyconsolidated from at least two of a plurality of frac tanks into asingle return header.
 16. The method of claim 1 wherein the chlorinedioxide free residual level is between about 0.25 ppm and about 5.0 ppm.17. The method of claim 1 further comprising logging and storingphysical and compositional parameters of the aqueous fluid on acontinuous, real-time basis.
 18. The method of claim 17 furthercomprising selectively reporting the stored physical and compositionalparameters.
 19. The method of claim 1 wherein sequential treatmentpoints are provided to facilitate continuous, real-time trimming of thechlorine dioxide free residual level.